In optical design for indoor lighting products light source brightness and the shaping of the light beam need to be considered. A too high brightness in the lighting product is not desired. It may cause an uneven light distribution from the lighting product which may provide scattering and beam shaping problems. A common lighting product (1) according to prior art is shown in FIG. 1 comprising a light source (2) and a scattering sheet (4) arranged on a distance (6) from the light source. A solid angle (8) represents the angle of the light from the light source covered by the scattering sheet.
Commonly in indoor lighting products there is a tradeoff between the light source brightness and the beam shaping ability of the lighting product. With high light source brightness, there may be problems in shaping the beam in a desired way. Further, low light source brightness may affect the effectiveness of the lighting product.
One way of solving the problems of reaching a suitable brightness level in accordance to the beam shaping in the lighting product is to first lower the brightness of the light from a light source, e.g. by adding a diffusing or scattering member arranged close to the light source. Subsequently is the light beam shaped, e.g. by a large reflector or white cup.
One example of such solution is disclosed in JP2010113975 wherein a diffusion sheet is arranged above a plurality of light emitters. To shape the light beam a light beam shaper needs to be added, such as a reflector.
In an alternative way, the light beam is first shaped, e.g. by TIR (Total Internal Reflection) collimators or a small reflector, and subsequently the light brightness is reduced, e.g. by introducing a limited diffusive exit window for the light beam.
Further, there is a need to accomplish a minimal physical size of lighting products. As seen in FIG. 1b, a scattering sheet (4) may be arranged at a smaller distance (6′) to the light source (2), thereby both providing a larger solid angle (8′) and a smaller product. However, there is a limit to how small a lighting product with a reflector and a scattering sheet may be since there is a limit to how close a scattering sheet may be arranged to a light source without exceeding a maximum brightness. Such arrangement may cause a too high brightness level in a central portion of the scattering sheet, and a significantly lower brightness level in edge portions of the scattering sheet. This may cause an uneven light distribution that negatively affects the beam shaping abilities of the lighting product.
Consequently, there is a need for an alternative solution for a lighting product of smaller size, which combines moderated brightness with beam shaping ability.